Effects Of Deficit Irrigation On Soil CO₂?N₂O And CH₄ Emissions From Winter Wheat-summer Maize Rotation Fields

Farmland Greenhouse gases?GHGs?emission peak and total amounts could be affected by the degree of water deficit and irrigation time.In order to find a reasonable irrigation practice for farmland GHGs emission reduction,the static box-gas chromatography method was used to monitor the GHGs?CO₂,N₂O and CH₄?emission fluxes under winter wheat-summer maize rotation system in Guanzhong plain,Shaanxi province of China.In the paper,three irrigation levels?100%W;80%W;60%W?were set at three growth stages of winter wheat?overwintering,jointing and heading stage?and four growth stages of summer maize?seedling,jointing,heading and grouting stage?.Hence,six treatments were obtained?CK?T1?T2?T3?T4?T5,and CK treatment was full irrigation treatment?.The one year?2016.10-2017.10?field experiment was carried out to explore the characteristics of dynamic change for GHGs?CO₂,N₂O and CH₄?in the whole year,and to comprehensively evaluate the effects of water deficit levels in different crops stages on the economic and ecological effects of winter wheat and summer maize,using three indicators of crops yield,long-term warming effect?net GWP_L?and seasonal warming effect?net GWP_S?.?1?Soil respiration was significantly positive correlated with soil temperature?T?and water filled pore space?WFPS?,which they influence soil respiration coordinately.Comprehensive considering of T and WFPS could improve the prediction accuracy of soil respiration.Soil N₂O emission flux was significantly positive correlated with soil WFPS,T and soil NO₃^--N content?P<0.05?,among which NO₃^--N was the dominant factor affecting farmland soil N₂O emission.However,the main influencing factors of soil CH₄ emission flux in wheat and maize farmland have not been fully detected,which need to be explored in the following experiments.?2?Soil CO₂ and N₂O emission fluxes in farmland was generally showed the highest value was all appeared with CK treatment in different growth stages of wheat and maize.Deficit irrigation could significantly reduce soil CO₂ and N₂O emissions,while decrease soil CH₄ absorption fluxes.Taking the winter wheat jointing stage as an example,soil CO₂ emission flux with CK treatment was 97.39 mg·?m²·h?^-1,highest value among all treatments.Compared with CK treatment,soil CO₂ emission flux of T3 treatment was decreased by 5.68%?P>0.05?,T1,T4and T5 treatments,mild water deficit,were significantly reduced by 18.52%?20.26%and24.91%?P<0.05?,while T2 with severe water deficit treatment was significantly decreased by 33.39%?P<0.05?;And compared with CK treatment,soil N₂O emission flux of T3treatment was decreased by 3.84%?P>0.05?,T1,T4 and T5 treatments were significantly reduced by 18.66%?17.55%and 16.93%?P<0.05?,T2 treatment was significantly decreased by 26.92%?P<0.05?;As for soil CH₄ emission,the average CH₄ absorption fluxes with T1,T2,T4 and T5 were significantly increased by 74.04%,116.51%,77.24%and 85.69%?P<0.05?,comparing with treatment of CK.?3?The jointing stage,heading stage and filling stage of wheat are the key periods for reducing greenhouse gas emission,deficit irrigation could reduce the total amount of GHGs emission,reduce crops yield and mitigate the greenhouse effect to a certain extent.Compared with CK treatment,total CO₂ and N₂O emissions of other treatments were significantly reduced by 5.55%-25.98%?P<0.05?,and 5.63%-18.00%?P<0.05?,and total CH4 absorption was significantly increased by 19.47%-62.33%?P<0.05?during the wheat growing season.Compared with CK,the net GWP_L of T1,T2,T3,T4 and T5 was significantly reduced by 6.50%-12.77%;The net GWP_S of T1,T2,T4 and T5 were significantly reduced by 13.21%-37.65%?P<0.05?;The wheat yield under T1,T2,T4 and T5 treatment was significantly reduced by 2.25%-32.53%?P<0.05?,and the yield of T3treatment was reduced by 2.25%?P>0.05?.During the maize growing season,total CO₂ emissions under different treatments were ranged 5435.40-6356.92 kg·hm^-2,in which total CO₂ emission of T2 treatment was showed the significant reduction compared with CK treatment.The variation range of soil N₂O emissions for all treatments were between 1157.08-1306.79 g·hm^-2,showing the highest value of CK treatment.Compared with CK treatment,soil N₂O emissions of T1,T3,T4 and T5 treatments were reduced by 1.17%-7.62%?P>0.05?,while T2 treatment was significantly reduced by 11.46%?P<0.05?.The soil CH₄ absorptions were varied between 2414.00 and2926.45 g·hm^-2,displaying the lowest value for CK treatment and the highest value for T2treatment but no significant differences amount the treatments.Compared with T5,treatment for highest value of net GWP_L,net GWP_L of CK,T1 and T4 treatments were reduced by7.60%,2.71%and 0.10%?P>0.05?,while T2 and T3 treatments were significantly decreased by 13.07%and 15.85%?P<0.05?,respectively.The net GWP_S was showed the highest value for T3,followed by CK,and the lowest value for T4.Taking into comprehensive consideration of economic and ecological effects of wheat field under the practice of water deficit level applied in different crops growth stages,T3treatment seemed to be more effective to the crops yield conservation,water saving and GHGs emission reduction of winter wheat and summer maize in Guanzhong plain.